Master cylinder for hydraulic braking system

ABSTRACT

This invention relates to a master cylinder for hydraulic braking system including a cylinder body, a bore formed in the body, a fluid displacing piston slidably mounted within the bore and having primary and secondary cups, a poppet valve interposed between a reservoir and a chamber formed in the bore for closing communication between the reservoir and the chamber against the fluid pressure in the chamber and for opening the communication therebetween against the fluid pressure in the reservoir, the poppet valve and the secondary cup act with the primary cup to form an airtight chamber filled with oil, a first warning of device for warning the failure of the primary cup, a second warning device for warning that the level of the brake fluid in the reservoir is low, and a third warning device for warning when the pressure the brake fluid in the reservoir is below a certain pressure.

United States Patent 191 'Wada I [4 1 Feb. 12, 1974 1 1 MASTER CYLINDERFOR HYDRAULIC BRAKING SYSTEM [75] Inventor: Takeshi Wada, Toyota City,Japan [73] Assignee: Aisin Seiki Kabushiki Kaisha,

Tokyo, Japan [22] Filed: Apr. 17, 1972 [21] Appl. No.: 244,653

[30] Foreign Application Priority Data May 1, 1971 Japan 46/29010 May15, 1971 Japan.. 46/32661 May '19, 1971 Japan 46/33776 [52] US Cl 340/52C, 188/1 A, 200/82 D, 340/59, 340/244 E [51] Int. Cl B60q l/44, B60t11/22 [58] Field of Search. 340/52 C, 59, 60, 240, 244 E; 200/82 D, 83J; 188/345, 1 A, 152, 345

[56] References Cited UNITED STATES PATENTS 2,566,545 9/1951 Alcoriza200/83 J 2,824,187 11/1958 Fanning..... 340/244 E 3,064,432 ll/l962Shutt 188/345 Reznicek 340/52 C Wing et a1 340/52 C [57] ABSTRACT Thisinvention relates to a master cylinder for hydraulic braking systemincluding a cylinder body, a bore formed in the body, a fluid displacingpiston slidably mounted within the bore and having primary and secondarycups, a poppet valve interposed between a reservoir and a chamber formedin the bore for closing communication between the reservoir and thechamber against the fluid pressure in the chamber and for opening thecommunication therebetween against the fluid pressure in the reservoir,the poppet valve and the secondary cup act with the primary cup to forman airtight chamber filled with oil, a first warning of device forwarning the failure of the primary cup, a second warning device forwarning that the level of the brake fluid in the reservoir is low, and athird warning device for warning when the pressure the brake fluid inthe reservoir is below a certain pressure.

7 Claims, 3 Drawing Figures ml 1.8 4o 1.1 1. 36 W 46 3 PAIENIEU FEB 1219'.

SHEEI 1 OF 3 MASTER CYLINDER FOR HYDRAULIC BRAKING SYSTEM BACKGROUND orTHE INVENTION This invention relates to improvements in and relating toa master cylinder, especially adapted for use on automotive vehicles.

Generally speaking, a conventional master cylinder of the fluiddisplacing piston type is provided with a brake system so that apressure responsive switch dis-.

posed in a fluid pressure circuit between the master cylinder and abrake wheel cylinder is switched on when the fluid pressure circuit isdamaged, so that the driver of-vehicle is warned of the abnormality ofthe fluid pressure circuit. However, in this master cylinder there is noprovision of means for detecting damage to the sealing cup on thepressurized-side by the piston and for warning the driver of vehicle,and further the fluid pressure to the brake wheel cylinder cant beincreased by this system when this cup is damaged. These deficienciesare considered to be greatly disadvantageous in practice.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide an improved master cylinder for a hydraulic brakingsystem adapted for obviating the aforementioned drawbacks ofconventional master cylinders.

It is another object of the present invention to provide an improvedcylinder for a hydraulic braking system capable of obtaining the samebraking force as that normally obtained by the depression of a brakepedal even in the case'of damage to the sealing cup and for sealing onthe pressurized side by a piston and for sealmg.

It is still another object of the present invention to provide animprovedv master cylinder for a hydraulic braking system capable ofdetecting damage to the sealing cup.

It is a further object of the present invention to provide an improvedmster cylinder for a hydraulic braking system capable of detecting whenthe level of the brake fluid within reservoir tank becomes low.

It is still a further object of the present invention to provide animproved master cylinder for a hydraulic braking system capable ofdetecting when the fluid pressure within the reservoir is below acertain pressure.

BRIEF DESCRIPTION OF THE DRAWING Various other objects, features andattendant advantages of this invention will be more fully appreciated asthe same becomes better understood from the following detaileddescription when considered in connection with the accompanyingdrawings, in which:

FIG. 1 is a sectional view taken axially through the master cylinder andassociated elements with warning means and their components with themaster cylinder diagrammatically illustrated.

FIG. 2 is a view similar to FIG. 1, showing a modified form ofmechanism, namely, a tandem master cylinder; and

FIG. 3 is a view similar to FIG. 2, showing an another modified form ofmechanism.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1 of theaccompanying drawings, the first embodiment of the invention will bedescribed hereinbelow in detail.

In this FIG. 1, the numeral 10 denotes a master cylinder fixed to orsubstantially integral with an upper reservoir 11. The master cylinder10 includes a cylinder body 12, a bore 13 formed in the body 12, and afluid 0 displacing piston 14 axially slidably mounted within the bore13, and provided at both ends with primary and secondary annular sealingcups 15 and 16 respectively. The outer end of the piston 14 is axiallyrecessed for receiving the end of a push rod 17 through which force isapplied to the piston 14 by direct operation of a brake pedal 18. Achamber 19 is formed between the inner end wall of the piston 14 and aninside wall of the body 12. A return spring 20 interposed within thechamber 19 urges the piston 14 to the right as viewed in FIG. 1. Thechamber 19 is always connected to brake wheel cylinders, of which onlyone is shown representatively at 21, through a conduit 22. The body 12is provided with an outlet port 23 for communicating the fluid pressurewithin the chamber 19 to the brake wheel cylinder 21. An annular chamber24, extending axially along a portion of the piston 14, communicateswith the reservoir 11 via a port 25.

A poppet valve 26, being interposed between the annular chamber 24 andthe chamber 27 of the reservoir 1 1 through the port 25 and having firstand second protruding portions 28 and 29, is in contact with aprojecting flange portion 30 formed on the outer peripheral surface ofthe piston 14. A spring 31 is disposed within the chamber 27 and one endof the spring 31 contacts the first protruding portion 28 of the poppetvalve 26 and other end thereof contacts a bottom portion 32 of thereservoir 11. The poppet valve 26 is urged upwardly by the spring 31 andoperates to close the communication between the annular chamber 24 andthe chamber 27 by causing the protruding portion 29 to en gage theannular valve seat of the bottom portion 32. The port 25 is opened bythe poppet valve 26 when the depressing force of the brake pedal 18 isnot applied and the port 25 is closed when the depressing force of thebrake pedal 18 is applied, namely,the poppet valve 26 is so constructedthat communication between the annular chamber 24 and the chamber 27 isclosed when the piston 14 is moved to the left from the position shownin FIG. 1, namely, when the lower end of the poppet valve 26 and theprojecting flange portion 30 of the piton 14 are disengaged.

A first compensating port 33 formed in the body 12 permits the brakefluid supplied from the reservoir 11 to pass to the chamber 19 and asecond compensating port 34 formed on the left end of the piston 14 iscapable of passing brake fluid within the annular chamber 24 from behindthe primary cup 15 to the chamber 19. Upon releasing brake action thebrake fluid within the annular chamber 24 passes into the chamber 19from behind the contracted cup 15 through the second compensating port34 while the first compensating port 33 is closed the piston 14 movingfrom the left position toward the right. The second compensating port 34operates particularly efficiently when the pumping of the piston 14 iscaused by double brake action and when the piston 14 is rapidly returnedfrom the forward or left position. The fluid pressure within the annularchamber passes to the chamber 19 through the first compensating port 33when the piston 14 is returned to the right position as viewed inFIG. 1. Numeral 35 is a snap ring positioned in an annular groove at theright hand end of the bore 13 for regulating the rightward movement ofthe piston 14 as viewed in FIG. 1.

Numeral 36 is a pressure responsive switch fluidically connected to anoutlet port 37 formed on the body 12 through a conduit 38, and a warninglamp 39 connected to the pressure responsive switch 36 through a wire 40is lighted in responsive to the signal from the pressure responsiveswitch 36. A source of electricity 41 is connected to the warning lamp39 through a wire 42 and is connected to ground 43 through a wire 44.Numeral 45 is the ground connected to the pressure responsive switch 36through a wire 46. The pressure responsive switch 36 operates when thefluid pressure within the annular chamber 24 is increased, for example,by failure of the primary cup 15. An electric circuit, namely, theground 45, the pressure responsive switch 36, the warning lamp 39, thesource of electricity 41 and the ground 43 is made and the warning lamp39 is lighted.

An insulator 47 placed on the upper end of the reservoir 11 has a port48 at the center thereof and a port 49. A cap 50 is placed on the upperend of the insulator 47 and a float member 51 is disposed within thechamber 27 and is provided with a contact 52 of a float switch 53 madeof metal to normally contact with the cap 50. The other end of switch 53is connected to the float member 51 through the port 48. A chamber 54formed by the insulator 47 and the cap 50 communicates with theatmosphere through the port 49. Contact points 55 and 56 formed on theupper surface of the insulator 47 are contacted by the contact 52 whenthe float member 51 is lowered by decrease of the brake fluid within thechamber 27. A wire 57 connected to the contact point 55 is connected toground at 58 and awire 59 connected to the contact point 56 is connectedto the wire 40. An electric circuit, that is to say, ground 58, thecontact point 55, the contact 52, the contact point 56, the warning lamp39, the source of electricity 41 and ground 43 is made and the warninglamp 39 is lighted. Numeral 60 denotes an annular seal.

FIG. 1 illustrates the normal positions of the elements of the mastercylinder at a time when the vehicle brakes are not applied. The piston14 is held in an extreme right-hand position against the snap ring 35.The left edge of the primary sealing cup is positioned slightly to theright of the first compensating port 33. With the elements in thepositions described fluid from the reservoir 11 fills the chambers 19and 24.

The operation of the master cylinder 10 so far shown and described is asfollows:

When the driver of the vehicle depresses the brake pedal 18, the piston14 is moved against the biasing force of the spring to the leftwarddirection through the rod 17 in FIG. 1. Responsive to this movement ofthe piston 14, the lower end of the poppet valve 26, in contact with theprojecting flange portion 30 of the piston 14 becomes vertical by forceof the spring 31 and the communication between the chambers 24 and 27 isclosed when the protruding portions 29 engage the annular valve seat ofthe bottom portion 32. The fluid pressure within the chamber 19 ishermetically sealed by the operation of the primary cup 15 and isincreased. This increased fluid pressure within the chamber l9 isdelivered to the brake wheel cylinder 21 through the conduit 22 so thatthe brake is applied.

During this operation, the pressure responsive switch 36 does notoperate and the warning lamp 39 is not lighted because the volume of thechamber 24 is not varied.

When the driver of the vehicle releases the brake pedal 18, the piston14 is returned by the return spring 20 as seen in FIG. 1 and the fluidpressure within the chamber 24 communicates with the chamber 19 throughthe first compensating port 33.

Should a hydraulic failure occur in the primary sealing cup 15 duringbraking of the vehicle, the increased fluid pressure within the chamber19 will communicate with the annular chamber 24 through the secondcompensating part 34 and then the chambers 19 and 24 will behermetically sealed by the secondary sealing cup 16 so that the fluidpressure within the annular chamber 24 is increased so that the samenormal fluid pressure is applied to the brake wheel cylinder 21, and thepres sure through the conduit 38 is actuated to light the warning lamp39 and warn the driver of the vehicle that a hydraulic failure hasoccurred in the primary sealing cup 15. During this time, the same fluidpressure is communicated to the wheel brake cylinder 21 through theconduit 22 as normally and the brake is applied.

Moreover, upon releasing the brakes the pressure in the chamber 19 isreduced when the piston 14 move backwardly from the forward position.Against the re duced pressure the fluid pressure within the annularchamber 24 is communicated to the chamber 19 through the secondcompensating port 34. The backward movement of the piston 14 continuesuntil the poppet valve 26 opens and the brake fluid passes from thechamber 27 to the annular chamber 24 through the port 25.

When the quantity of fluid decreases within the chamber 27 of thereservoir 11, for example, by the excessive wear of brake shoe 21', thecontact 52 of the float switch 53 contacts the contact points 55 and 56to close the electric circuit from ground 58, 43 to ground and thewarning lamp 39 is lighted so that the driver of the vehicle is warnedthat some abnormality has occurred.

Next referring to FIG. 2, numeral 10' denotes a second master cylindersimilar to master cylinder 10 as shown in FIG. 1, to form a tandemmaster cylinder. The construction and operation of the tandem mastercylinder are the same as that shown in FIG. 1 except as follows:

A fluid displacing piston 14' axially slidably mounted within a commonbore 13, is provided at its end with sealing cups 15', 16 and 16"respectively. The right end of the piston 14 contacts with one end ofthe return spring 20 disposed within the chamber 19 and the left endthereof contacts with one end of a return spring 20 disposed within achamber 19, and the other end of the return spring 20' contacts with thewall of the common body 12. The return spring 20 constantly urges thepiston 14' in the rightward direction. The chamber 19 is alwaysconnected to front brake wheel cylinder, of which only one is shownrepresentatively at 21", through a conduit 22'. The body 12 is providedwith an outlet port 23"for communicating the fluid pressure from thechamber 19' to the brake wheel cylinder 21".

When the driverof the vehicle depresses the brake pedal 18, the piston14 is moved against the biasing force of the spring in the leftwarddirection through the rod 17 as viewed in FIG. 2. Responsive to thismovement of the piston 14, the fluid pressure within the chamber 19 isincreased and the increased fluid pressure is delivered to the rearbrake wheel cylinder 21 through the conduit 22, while the piston 14' ismoved against the return spring 20 by the biasing force of the returnspring 20 and the increased fluid pressure withinthe chamber 19 to theleftward direction. By this movement of the piston 14, the fluidpressure within the chamber 19 is increased and the increased fluidpressure is delivered to the front brake wheel cylinder 21" so thatfront brakes are applied.

Referring now to FIG. 3, numeral 62 denotes a pressure device mounted onthe left side of the reservoir 1 1. FIG. 3 is different from FIG. 1 onlyin respect that FIG. 3 has no float switch, and the construction andoperation of this system are same as that in FIG. 1 and these areomitted except follows:

A first cylinder 63 of the pressure device 62 is connected to the leftside of the reservoir 11 and a second cylinder 64 is connected to theleft end of the first. cylinder 63. The periphery of a diaphragm piston65 is fixed between the first and second cylinder 63, 64, and one end ofa piston rod 66 protrudes into the chamber 27 ofthe reservoir 11. Avacuum chamber 67, formed by the diaphragm piston 65 and a wall of thefirst cylinder 63, is made airtight by a seal 68 formed in the wall ofthe first cylinder 63. A chamber 69 formed by the diaphragm piston 65and the left end wall of the second cylinder 64 and always communicatesto the atmosphere through a port 70. A diaphragm 71 is supported on theright end of the piston rod 66 by means of a nut 72, and a chamber 73 isformed by the diaphragm 71 and the wall of the first cylinder 63 andcommunicates to the atmosphere through a port 74.

The vacuum chamber 67 is connected to a regulator valve 75 through aconduit 77. The regulator valve 75 is connected to an intake-manifold 78of an engine, not shown, through a conduit 79. The rightwardly airpressure acting on the diaphragm piston 65 moves the piston rod 66 tothe rightward direction against the biasing force of a spring 8t) ofwhich one end contacts the end wall of the first cylinder 63 and theother end contacts the diaphragm piston 65. The chamber 27- is kept at acertain pressure during the engine driving. The diaphragm piston 65,mounted on the left end of the piston rod 66, is supported by a nut 81,and a plate 82 is supported by a nut 83 and the nut 81 at the left endof the piston rod 66. The plate 82 disposed within the chamber 69contacts a contact point 84 formed on the second cylinder 64 having aninsulator 85 when the level of the brake fluid is uncommonly lowered byexcessive wearing of the brake shoe 21 of the brake wheel cylinder 21 sothat the diaphragm piston 65 is moved in the rightward direction.Consequently, an electric circuit, namely, the plate 82, the contactpoint 84, a wire 86, a warning lamp 39, the source of electricity 41 andground 43, is completed and the warning lamp 39 is lighted.

Numeral 87 and 88 are supporting means for supporting the diaphragmpiston 65 and the diaphragm 71, respectively. A bleeder 90 for releasingair is mounted on the top end of the reservoir 11 and has a passage 91therein. Numeral 92 is a port formed on the reservoir l1 and isconnected to a pressure responsive switch 93 through a conduit 94. Theswitch 93 is connected to the warning lamp 39. The pressure responsiveswitch 93 operates when the fluid pressure system from the reservoir 11to the brake wheel cylinder 21 is damaged so that the fluid pressurewithin the chamber 27 falls below a certain pressure. Consequently, thepressure responsive switch 93 is actuated, and the warning lamp 39 islighted.

Obviously many changes and modifications of the present invention arepossible in light of the foregoing teachings. It is to be understood,therefore, that within the scope of the appended claims, the inventionmay be practiced otherwise than specifically described herein.

What is claimed is:

l. A master cylinder for a hydraulic braking system having a fluidreservoir connected thereto comprising,

a cylinder body provided with a bore therein,

a piston axially slidably mounted in the bore of said cylinder body andoperably connected to a brake pedal, to provide a first chamber at oneend of said cylinder,

biasing means disposed within said first chamber for urging said pistonto the brake release position,

a primary and a secondary sealing cup mounted on opposed ends of saidpiston for providing seals between the bore and the piston, said pistonbeing provided with an annular recess between said sealing cups to forma second chamber,

a first passage for fluid communication between the reservoir and saidsecond chamber and a second passage for fluid communication between saidsecond chamber and said first chamber, said second passage beingcontrolled by said primary sealing cup,

a third passage formed in said cylinder body for fluid communicationbetween said first chamber, said second chamber and said reservoir, saidthird passage being closed when said piston is moved to increase thehydraulic pressure in said first chamber against said biasing means,

a poppet valve for controlling communication between the reservoir andsaid second chamber, and

means for closing said poppet valve when said piston is moved toincrease pressure in said first chamber and in said second chamber,

whereby said secondary sealing cup serves to pressurize said firstchamber when said primary sealing cup fails.

2. A master cylinder as claimed in claim 1 and further comprising afirst warning device responsive to failure of said primary sealing cup.

3. A master cylinder as claimed in claim 2, wherein said first warningdevice comprises a switch responsive to an increase in pressure of thefluid within said second chamber, and a warning lamp responsive to saidpressure responsive switch.

4. A master cylinder as claimed in claim 2 and further comprising asecond warning device responsive to the level of the fluid in thereservoir when it falls below a predetermined level.

5. A master cylinder as claimed in claim 4 wherein said second warningdevice comprises a float movable in response to the vertical movement ofthe fluid surface within the reservoir, a contact switch, said floatclosing said contact switch when said float is lowered said thirdwarning device comprises a diaphragm piston operable when the fluidwithin the reservoir is decreased, a plate connected to said diaphragmpiston, a contact switch, said plate closing said contact switch whensaid plate is moved with said diaphragm piston,

and a warning lamp responsive to said contact switch.

1. A master cylinder for a hydraulic braking system having a fluidreservoir connected thereto comprising, a cylinder body provided with abore therein, a piston axially slidably mounted in the bore of saidcylinder body and operably connected to a brake pedal, to provide afirst chamber at one end of said cylinder, biasing means disposed withinsaid first chamber for urging said piston to the brake release position,a primary and a secondary sealing cup mounted on opposed ends of saidpiston for providing seals between the bore and the piston, said pistonbeing provided with an annular recess between said sealing cups to forma second chamber, a first passage for fluid communication between thereservoir and said second chamber and a second passage for fluidcommunication between said second chamber and said first chamber, saidsecond passage being cOntrolled by said primary sealing cup, a thirdpassage formed in said cylinder body for fluid communication betweensaid first chamber, said second chamber and said reservoir, said thirdpassage being closed when said piston is moved to increase the hydraulicpressure in said first chamber against said biasing means, a poppetvalve for controlling communication between the reservoir and saidsecond chamber, and means for closing said poppet valve when said pistonis moved to increase pressure in said first chamber and in said secondchamber, whereby said secondary sealing cup serves to pressurize saidfirst chamber when said primary sealing cup fails.
 2. A master cylinderas claimed in claim 1 and further comprising a first warning deviceresponsive to failure of said primary sealing cup.
 3. A master cylinderas claimed in claim 2, wherein said first warning device comprises aswitch responsive to an increase in pressure of the fluid within saidsecond chamber, and a warning lamp responsive to said pressureresponsive switch.
 4. A master cylinder as claimed in claim 2 andfurther comprising a second warning device responsive to the level ofthe fluid in the reservoir when it falls below a predetermined level. 5.A master cylinder as claimed in claim 4 wherein said second warningdevice comprises a float movable in response to the vertical movement ofthe fluid surface within the reservoir, a contact switch, said floatclosing said contact switch when said float is lowered a predeterminedamount, and a warning lamp responsive to said contact switch.
 6. Amaster cylinder as claimed in claim 2 and further comprising a thirdwarning device responsive to decreased fluid pressure within thereservoir below a predetermined value due to failure of fluid pressureat a brake cylinder.
 7. A master cylinder as claimed in claim 6, whereinsaid third warning device comprises a diaphragm piston operable when thefluid within the reservoir is decreased, a plate connected to saiddiaphragm piston, a contact switch, said plate closing said contactswitch when said plate is moved with said diaphragm piston, and awarning lamp responsive to said contact switch.